1. Field of the Invention
The invention relates to treatment of wastewater through a membrane to significantly reduce the size and number of particulates in the treated wastewater.
2. Description of the Prior Art
Biological treatment of wastewater often employs either activated sludge or fixed film processing steps. Activated sludge is the semi-liquid biomass removed from the liquid flow of wastewater, particularly from the liquid flow of wastewater. Before it is fully decomposed by aerobic microbial decomposition, activated sludge is put into aeration tanks to facilitate and further undergo aerobic microbial decomposition. Fixed film processes may use biological aerators that rotate around a central horizontal shaft, which is submerged in the wastewater. As the aerators reemerge from the surface of the wastewater, they catch air in specially profiled cells.
A typical activated sludge apparatus uses an aeration tank, also referred to as an aeration basin or biotank housing a cell segment contact aerator, and a separate settling tank or gravity clarifier, also referred to as a settling tank or gravity separator. See, for example, U.S. Pat. No. 6,039,873, to Stahler, the entire disclosure of which is herein incorporated by reference. The purpose of the clarifier is to remove the suspended solid particles in the wastewater. The solid particles range in size from microscopically fine to rather coarse, and consist primarily of undissolved or unoxidized material, spent bacteria and other microorganisms. The clarifier can be one of a number of types, including circular, hopper bottom or rectangular. In the prior art, however, they are all separate from the aeration tank.
In order to solve the deficiencies of conventional devices, rotary aerators have been developed. Exemplary rotary aerators or BIO-WHEEL and BIO-ROTOR devices available from Wastewater Technology, Inc. of Monterey, Va. are described by U.S. Pat. Nos. 6,572,774 and 6,613,229 to Ricketts, each of which is herein incorporated by reference in its entirety.
However, even when the rotary aerators are utilized, it has been difficult, if even possible to reduce particulates to (1) no more than 5 mg/L for BOD (biochemical oxygen demand, i.e., the concentration of biodegradable organic matter) and total suspended solids; (2) no more than 5 mg/L for total nitrogen; and (3) no more than 0.5 mg/L for total phosphorous.